Solvent process for production of composite propellants using hexane and hmx

ABSTRACT

A &#34;SOLVENT&#34; PROCESS FOR THE LARGE SCALE PRODUCTION OF THE COMPOSITE PROPELLANTS EMPLOYING HMX AS AN OXIDANT WHEREBY A MIXTURE OF HMX AND N-HEXANE IS INTIMATELY MIXED WITH A BINDER MIXTURE AND THE N-HEXANE SUBSEQUENTLY REMOVED FROM THE PROPELLANT MIXTURE BY VACUUM EVAPORATION.

Patented Sept. 10, 1974 3,834,957 SOLVENT PROCESS FOR PRODUCTION OF COM- POS}I{TE PROPELLANTS USING HEXANE AND HM John P. McDevitt, Accokeek, and Marguerite S. Chang, Forest Heights, Md., assignors to the United States of America as represented by the Secretary of the Navy No Drawing. Filed May 14, 1970, Ser. No. 48,770 Int. Cl. C06d /06 US. Cl. 149-194 10 Claims ABSTRACT OF THE DISCLOSURE A solven process for the large scale production of the composite propellants employing HMX as an oxidant whereby a mixture of HMX and n-hexane is intimately mixed with a binder mixture and the n-hexane subsequently removed from the propellant mixture by vacuum evaporation.

BACKGROUND OF THE INVENTION This invention generally relates to a composite propellant production process and more particularly to a process for producing a composite propellant comprising cyclotetramethylenetetranitroamine (HMX).

Recent developments in the field of cartridge activated devices, specifically in the field of emergency personnel escape devices, have generated a need for a propellant characterized not only by high impetus and high burning rate, but also by high thermal stability 300 F.).

A composite propellant satisfying these hereinbeforeidentified needs has been disclosed by Chang et al. in US. Patent aplication Ser. No. 839,802 filed July 1, 1969. This composite propellant is comprised of any elastomeric, plastic or resinous binder material and a new oxidant admixture of HMX, potassium perchlorate and lead chromate as a burning rate modifier. The discovery of such a desirable propellant, created a need for the development of a process for the large scale production thereof.

The hazards of handling HMX is well known to those skilled in the propellant art. In fact, HMX normally is handled and transported in an aqueous solution to reduce the hazard. However, water is usually not tolerated in composite propellant systems because of its weight, while dry HMX, especially in large quantities, is too dangerous to handle.

Generally, composite propellants are produced by a solventless mix process. However, in the case of HMX containing composite propellants such a solventless mix process, especially on a large scale production, becomes an unacceptable safety hazard due to a number of reasons among which are the inherent dangers of handling dry HMX and the danger due to friction generated during the solventless mix process wherein the temperature approaches the decomposition point of the HMX.

SUMMARY OF THE INVENTION Accordingly, it is one object of this invention to provide a process for the production of an HMX containing com posite propellant.

It is another object of the present invention to provide a process for the large scale production of an HMX containing composite propellant.

Another object of the instant invention is to provide a solvent mix process for the production of an HMX c0ntaining composite propellant.

It is still a further object of the present invention to provide a solvent mix process for the large scale production of an HMX containing composite propellant which is safe and yields a propellant with the same desirable physical properties, thermal stability as well as burning characteristics as one manufactured in a solventless mix process.

These and other objects are achieved by a solven process wherein a mixture of HMX and n-hexane is thoroughly mixed into a pre-mixed binder mixture and the n-hexane is subsequently removed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the present invention is useful in the production of HMX containing composite propellants and especially those propellants disclosed in US. application Ser. No. 839,802 filed July 1, 1969 by Chang et al. which is a continuation-in-part of the US. application Ser. No. 643,292 filed May 23, 1967.

The composite propellants disclosed therein employ any elastomeric, plastic or resinous binder as the fuel matrix such as polyurethanes, polysulfide rubber, polyvinylchloride, epoxy resins, polyesters, hydrocarbon rubber, asphalt, acrylic polymers. More specifically some of these are polymers of butadiene and acrylic acid such as Butarez CTL-II, terpolymer of 2-methyl-5-vinyl-tetrazole/ethyl acrylate/ acrylic acid, polyglycol adiphate and epoxy resins such as Epon 812, the digylcidyl ether of bisphenol A. These binders are cured with any of the common crosslinking agents such as EPN-ll38, a triepoxide made by Ciba Chemical Company, New Jersey, a diepoxide (MAPO) trimethylaziridinyl phosphine oxide and chromium naphthenate, and the like.

The oxidant component of the propellant is a mixture of HMX and potassium perchlorate. Preferably, the nitramine component is mixed with the potassium perchlorate in a ratio of 19:1 to 1.221. More preferably, however, is the admixture of from -60 parts by weight nitrate with 10-30 parts by weight potassium perchlorate.

The oxidant mixture is generally present in amounts of from about 50-95 parts per parts of propellant and, more preferably in amounts of from almost 80-95 parts per 100 parts of propellant.

Other additives normally incorporated into solid oxidants and composite propellants may also be added therein, such as any of the various accelerators, burning rate catalysts, extenders, reinforcing agents and fillers. A preferred burning rate modifier is lead chromate (PbCr04).

Thus, according to the present process these and other HMX containing composite propellants are produced by mixing the desired binder material with the cross-linking agent, curing agent, curing catalyst, burning rate modifiers, or any of the other additives normally incorporated as disclosed hereinabove until the mixture is substantially homogenous.

Generally, homogeneity is evidenced by the overall liquidy nature and the lack of any aggregate lumps in the mixture. Normally, but depending upon the quantities of materials employed and also the speed of the mixing action, the mixture is hom'ogenous in about 5-10 minutes after mixing begins. This initial mixing and all subsequent mixing performed in the present process is prefenably carried out at a temperature from about -120 F. in a conventional vertical propellant mixer, such, for example, a Baker-Perkin Vertical Mixer. However, any similar type mixer, which is capable of vacuum adaptation and provides a kneading action such as the horizontal propellant vacuum mixer also may be employed.

Furthermore, it is not advisable to utilize a much lower or higher temperature than as set forth hereinabove during mixing since a lower temperature will normally affect a higher viscosity mixture and require 'a longer mixing time while a higher temperature will normally initiate premature curing of the binder.

After the initial binder material mixture reaches homogeneity and upon continued mixing a mixture of HMX and n-hexane is added thereto. This mixture of HMX and n-hexane is preferably comprised of from about .5-1 part by weight of n-hexane to about 1 part by weight of HMX. However, any amount of n-hexane capable of wetting all the particles of HMX is operable for the purposes of this invention. Although it is within the scope of the present invention, the total HMX-n-hexane mixture is not added to the initial binder mixture at one time, but for safety reasons is added in portions with mixing after each additional portion until the characteristic white color of the HMX has disappeared (about 3 to 5 minutes). At this stage the total propellant mixture is characterized by a pasty, doughy and high viscosity consistency.

With continued mixing, any additional oxidants, such as potassium perchlorate, which is utilized in the composite propellants especially prepared by the present process, are then added to the propellant mixture. Of course other inorganic oxidants may be added, e.g., ammonium perchlorate, lithium perchlorate, ammonium nitrate, lithium nitrate and the like. Normally, this mixing period is performed at least until the characteristic color of the potassium perchlorate or other oxidant has disappeared (about 3 to 5 minutes). It is also within the scope of this invention to add any of the traditional materials as set forth hereinabove, such as burning rate modifiers, accelerators, burning rate catalysts, extenders, etc., to the propellant mixture at the same time as any of these additional oxidants, rather than in with the initial binder materials.

At this point, the total propellant mixture is subjected to continuous mixing until the propellant achieves substantial ballistic property consistency. Generally, this is attained from about /2 hour to about 1 hour of mixing after the last ingredients have been added.

The n-hexane solvent is then removed from the propellant mixture by vacuum evaporation at the temperature employed during the mixing operations. The remaining propellant mixture is then either cast or extruded using conventional means and cured.

The general nature of the invention having been set forth, the following examples, are presented as specific illustrations thereof. It will be understood that the inven tion is not limited to these examples but is susceptible to various modifications that will be recognized by one of ordinary skill in the art.

Example 1 A 4 pound propellant composition consisting of 69.0% HMX, 15.0% potassium perchlorate, 12.3% polyglycol adipate, 1.64% Kopox-170 (a trifunctional epoxide made by the Koopers Company, Pittsburgh, Pa.), 0.06 ferric acetylacetonate (FeAA) and 1.0% copper chromite was manufactured according to the following procedure: 223.6 grams of polyglycol adipate, 29.9 gram-s of Kopox-170 and 0.9 grams of FeAA were mixed together for five minutes at the first speed in a Baker-Perkin Vertical Mixer under a full vacuum. Releasing the vacuum, 436.2 grams of HMX having an average particle size of 150 microns and previously wetted with 289.1 grams of n-hexane (i.e. a 3:2 ratio of HMX to n-hexane) was added in two equal portions to the polyglycol adipate binder mixture in the mixing apparatus. The mixing was continued for 3 minute cycles after each addition of HMX-n-hexane. Then, 817.6 grams of HMX having an average particle size of 25 microns which was also previously wetted with 545.1 grams of u-hexane (3:2 ratio) was also added in two equal portions to the mixing apparatus at three minute mixing cycles. The process was continued by adding and mixing with the propellant for three minutes 272.6 grams of potassium perchlorate, after which time 36.4 grams of copper chromite was added to the propellant and also mixed in a three minute cycle period. At this point to insure intimate admixture of all the ingredients the total propellant composition was thoroughly mixed for an additional 25 minutes. After this the n-hexane was removed by vacuum and collected. The propellant composition was removed from the mixing apparatus, extruded and cured at 203 F. for 3 days. The total mixing process was performed at a temperature of from about 93 to about 123 F.

Example 2 A 35 pound propellant composition consisting of 69.0% HMX, 15.0% potassium perchlorate, 12.3% polyglycol adipate, 1.64% Kopox170, 0.06 ferric acetylacetonate and 1.0% lead chromate (PbCrO was manufactured according to the following procedure: 4.30 pounds of polyglycol adipate, 0.58 pounds of Kopox-170 and 9.53 grams of FeAA were mixed together for five minutes at the first speed in a Baker-Perkin Vacuum Mixer under a full vacuum. Releasing the vacuum, 15.40 pounds of HMX having an average particle size of 25 microns and previously wetted with n-hexane in a 3:2 Weight ratio was added in two equal portions to the polyglycol adipate binder mixture in the mixing apparatus. The mixing was performed for 3 minute cycles after each addition of HMX-n-hexane. Then 8.75 pounds of HMX having an average particle size of 18 microns which was also previously wetted with n-hexane in a 3:2 weight ratio was also previously wetted with n-hexane in a 3:2 weight ratio was also added in two equal portions to the mixing apparatus at three minute mixing cycles. The process was continued by adding and mixing with the propellant for three minutes 5.25 pounds of potassium perchlorate, after which time 0.70 pounds of lead chromate (PbCrO was added to the propellant and also mixed in a three minute cycle period. At this point to insure intimate admixture of all the ingredients the total propellant composition was thoroughly mixed for an additional 25 minutes. After this, the n-hexane was removed by vacuum and collected. The propellant composition was removed from the mixing apparatus extruded and cured. The temperature throughout the procedure varied from about F. to about F.

As will be evident to those skilled in the art, various modifications can be made in light of the foregoing disclosure without departing from the scope and spirit of the invention.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A method for producing a composite propellant containing cyclotetramethylene-tetranitroamine which comprises:

(a) thoroughly mixing a binder material selected from the group consisting of polysulfide rubber, polyurethane, polyvinylchloride, epoxy resins, polyesters, hydrocarbon rubber, asphalt, and acrylic polymers with a curing agent,

(b) adding and intimately mixing to the product thereof a mixture of cyclotetramethylenetetranitroamine and n-hexane and,

(c) removing said n-hexane 2. The method of claim 1 wherein a composite propellant additive selected from the group consisting of burning rate modifiers, extenders, reinforcing agents, fillers and mixtures thereof is also thoroughly mixed in step (a).

3. The method of claim 2 wherein an additional composite propellant inorganic oxidant is added to and intimately mixed with the product of step (b) prior to the removal of the n-hexane.

4. The method of claim 3 wherein said binder material is selected from the group consisting of poly(butadieneacrylic acid), the polymerization product of ethylenediamine and linoleic acid, the terpolymer of 2-methyl-5- vinyl-tetrazole, ethyl acrylate and acrylic acid, the diglycidyl ether of bisphenol A, and polyglycol adipate, said composite propellant additive is a burning rate modifier selected from the group consisting of lead chromate, copper chromite, lead salicylate, lead stearate and lead B- resorcylate and said additional composite propellant oxidant is potassium perchlorate.

5. The method of claim 3 wherein steps (a), (b) and '(c) are performed at a temperature within the range of from about 110-120 F.

6. The method of claim 3 wherein said mixture of cyclotetramethylene-tetranitro-amine and n hexane contains a sufficient amount of n-hexane to wet substantially all the particles of cyclotetramethylenetetranitroamine.

7. The method of claim 3 wherein the propellant mixture is extruded and heat cured subsequent to the removal of the n-hexane.

8. The method of claim 3 wherein the propellant mixture is cast and heat cured subsequent to the removal of the n-hexane.

9. The method of claim 1 wherein said mixture consists 1 part by weight of cyclotetramethylenetetranitroamine.

UNITED STATES PATENTS 6/1962 Bice 14992 X 8/1966 Visnov et a1. 14992 X 10 BENJAMIN .R. PADGETT, Primary Examiner US. Cl. XuR. 

